This invention relates to a dichlorobenzidine dihydrochloride slurry having both a low solid settling rate and a low viscosity. The invention also relates to a method for preparing such a slurry.
The chemical compound 3,3-dichlorobenzidine dihydrochloride, hereinafter referred to as DCB, is the primary ingredient used in the production of yellow pigments. The pigments so produced are used extensively in the printing industry as the predominant source of coloring for yellow ink.
DCB is produced as either a wet or a dry powder. It is then packaged in drums and shipped to the pigment manufacturer. To begin the pigment manufacturing process, the DCB is poured into large mixing tanks and then reacted with various other chemicals to yield a yellow compound.
Both the wet powdered and the dry powdered forms of DCB are very dusty. A substantial amount of DCB dust is generated throughout the packaging, shipping and pigment manufacturing processes.
In 1974, the Occupational Safety and Health Agency (OSHA) designated DCB as a "cancer suspect agent". Because of this designation, the handling and usage of DCB is strictly regulated (see 29 CFR 1910.1007).
The regulations promulgated by OSHA are designed to minimize human and environmental exposure to the DCB powder and dust. For example, 29 CFR 1910.1007 requires DCB to be handled in isolated structures which are fully enclosed and impervious to the passage of DCB. The isolated structure must be provided with a ventilation system which constantly pumps fresh air into the system and withdraws contaminated air from the system. The exhaust air, before it can be discharged back into the environment, must be scrubbed in order to remove any suspended DCB dust.
The regulations also require the drums containing the DCB to be unloaded under drum dusting hoods. The DCB contaminated air that is sucked up by the hoods must then be scrubbed before being discharged into the environment. Further, the drums must be decontaminated and disposed of after use. The solution used to rinse out the drums must also be decontaminated.
The regulations further require the employees who handle DCB powder to wear full protective clothing, including gloves, impervious body suits and air-supplied dust hoods, in order to minimize their exposure to DCB powder and/or dust. Working in such protective clothing is very cumbersome. Employees are also required to shower and change their clothes after working in an isolated structure where DCB is handled or used.
The handling of powdered DCB is an expensive and labor intensive process. In order to comply with OSHA regulations, substantial amounts of money must be spent to construct the isolated system, to purchase the ventilation and pollution control equipment, and to operate such facilities on a day-to-day basis.
Many of the problems associated with the handling of powdered DCB could be eliminated or reduced by making DCB available in a non-dusty form. The present invention provides a non-dusty DCB composition in the form of a DCB slurry.
A serious problem associated with liquid slurries is that such compositions have high solids settling rates. Slurries having high solids settling rates must be constantly stirred in order to keep the particles in suspension. If the slurry is not stirred, the particles that settle out will clog drains, pipes, filters and pumps.
Another serious problem associated with liquid slurries is that such compositions, in order to be economical, must have a high solids concentration. However, a slurry having a high solids concentration is usually quite thick and viscous. Thick, high viscosity slurries do not flow easily and thus are difficult to pump.
These problems associated with settling rates and viscosity are inter-related. One can attain a slurry having a low solid settling rate by increasing the slurry viscosity. However, such a slurry, while stable, is extremely difficult and expensive to pump. On the other hand, one can attain a fluid, low viscosity slurry by decreasing the concentration of the suspended solids or by adding thinning agents. However, such a slurry, while easy to pump, generally has a high settling rate.